This invention relates to a liquid-sealed antivibration device used for supporting a bivratory body such as an automobile engine in a vibration-proof manner.
Heretofore as a mount for supporting an automobile engine or any other vibratory body so as not to transmit its vibrations to the vehicle body or the like there have been known liquid-sealed type antivibration devices, wherein a liquid is sealed within a main body provided with a vibration-isolating base made of rubber elastomer.
For instance, JP Patent Publication 7-77234 (1995) A discloses a liquid-sealed antivibration device, in which a vibration-isolating base made of rubber elastomer and a diaphragm of rubber membrane are respectively attached hermetically to one opening and the other opening of a cylindrical main body fitting, an interior room enclosed by them is sealed with a liquid, a partition member having at its outer circumference an orifice is arranged between the vibration-isolating base and the diaphragm to compart into two upper and lower chambers, both liquid chambers being put into communication with each other through the orifice.
This liquid-sealed antivibration device is used by connecting a boss fitting, which is secured to the axial center of the vibration-isolating base, to a vibration source side and connecting the cylindrical main body fitting to a support side. And it is adapted to exhibit a vibration damping function and a vibration isolating fuction by reason of a liquid fluidization effect between both liquid chambers due to the orifice and a vibration absorbing effect due to the vibration-isolating base. Usually in order that the aforesaid orifice may exhibit an effective vibration damping function in a vibrational frequency region of shake vibration (10xcx9c15 Hz), its sectional area is determined and set.
With such a liquid-sealed antivibration device, an important requisite for obtaining stabilized reliable product characteristics with no dispersion is that the sectional area of an orifice adapted to shake vibration be set to conform to a desired dimension.
However the partition member of the antivibration device as disclosed above is prepared by press forming one steel plate to form a recessed channel at its outer circumferential part, and press fitted in the cylindrical main body fitting, whereby the orifice is formed between it and the inner peripheral surface of the main body fitting. Because of this, the dimensional precision of the aforesaid sectional area is not so high that a dispersion in characteristics of product is liable to occur.
The foregoing partition member was further fitted at its central area with an elastic membrane by vulcanization adhesive means and the reduction in dynamic spring rate was owed to one of the orifices (for shake vibration) and the aforesaid elastic membrane, and yet it was difficult to obtain a reduction effect in dynamic spring rate of vibrations generating a muffled sound in a relatively high frequency region (100 to 200 Hz).
In view of the aforementioned problems this invention has been made and is contemplated providing a liquid-sealed antivibration device with which it is possible to enhance the dimensional precision of the orifice at the outer peripheral portion corresponding to shake vibration, to reduce the dispersion in characteristics, and to lower the dynamic spring rate in a high frequency region and which is excellent also in reduction effect of noise such as a muffled sound or the like.
The liquid-sealed antivibration device of this invention is composed of an open bottom type of cylindrical main body fitting assuming a generally cup shape and having an open top, a boss fitting arranged inboard of the main body fitting in its axial center part, a vibration-isolating base of rubber elastomer interconnecting a lower part of the main body fitting and the boss fitting so as to close the bottom opening, a diaphragm of rubber membrane connected to the cylindrical main body fitting at its upper extremity so as to cover the open top, an interior room enclosed by these elements and sealed with a liquid, and a partition element arranged between the vibration-isolating base and the diaphragm to compart the interior room into a main liquid chamber on the boss fitting side and a first subsidiary chamber on the diaphragm side, both chambers communicating through an orifice with each other. And the device is characterized in that the partition element comprises a partition plate member including an elastic membrane at its central part and an orifice member disposed on the first subsidiary chamber side so as to contact with a peripheral edge portion of the elastic membrane in an opposing manner; a first orifice of a generally ring shape is formed by the orifice member, an outer peripheral portion of the partition plate member and a cylindrical rubber portion linking to the diaphragm; a space enclosed by a central plate section of the orifice member and a top surface of the elastic membrane is formed as a second subsidiary liquid chamber; the central plate section of the orifice member is formed with an opening as a second orifice for a muffled sound communicating from the first subsidiary chamber to the second subsidiary chamber.
Since the second orifice for a muffled sound on the first subsidiary chamber side as well as the first orifice at the outer periphery corresponsing to shake vibration are thus provided, it follows that the dynamic spring rate also in a higher frequency region (100xcx9c200 Hz) in comparison with the conventional device can be reduced. Accordingly it is possible to perform the vibration damping effectively in a wider frequency range thereby to enhance the effect of inhibiting noises. Furthermore on account of the construction that the first orifice is formed by the partition plate member and the orifice member, a formed or molded material can be utilized easily to either of them, so that it is possible to enhance the dimensional precision of the sectional area of the orifices and to reduce the dispersion in characteristics.
In the aforesaid liquid-sealed antivibration device, it is preferred that the opening as the second orifice, which the central plate section of the orifice member has, be at an opposite side to and made eccentric to the position of a communication part from the first orifice to the first subsidiary chamber. By this constitution it is possible to avoid mutual interference of both first and second orifices and further to stabilize the characteristics. In addition, even if the central portion of the diaphragm abuts on the central plate section of the orifice member when the first subsidiary chamber is contracted under diminished pressure, the second orifice is never choked.
In the preceding liquid-sealed antivibration device it is preferred that the partition plate member of the partition element be made of a metal plate by press forming, which is adhered, at its central opening part, with an elastic membrane such as rubber by vulcanization and that the orifice member be composed of a formed or molded body, e.g., of metal such as aluminum or its alloy, ceramic material or synthetic resin. By that constitution, it is possible to enhance the dimensional precision of the orifices.
Alternatively in the aforesaid liquid-sealed antivibration device, it is possible to construct so that the diaphragm is adhered by vulcanization to a cylindrical member fastened to the upper extremity at the open top of the cylindrical main body fitting; the cylindrical rubber portion integral with the diaphragm is fitted in an inner periphery of the cylindrical member; the orifice member and the partition plate member of the partition element are fitted in the inner periphery of the cylindrical rubber portion to form the first orifice. Thereby the bonding strength of the diaphragm can be enhanced.
Further, the aforementioned first orifice can be generally ring-shaped such that its circumferential path enclosed by outer circumferences of the partition plate member and orifice member and the cylindrical rubber portion is partly closed by a blocking wall portion, the blocking wall portion comprising a part of the orifice member and a rubber portion adhered by vulcanization to the partition plate member.
The liquid-sealed antivibration device as described above is used, with the boss fitting coupled to a vibration source member such as engine while with the cylindrical main body fitting coupled to a support side member such as a vehicle body.